1. Technical Field of the Invention
The present invention relates to tubing welders and, more particularly, to clip on unattended welders for forming a seal in a length of tubing to seal the tubing.
2. Description of Related Art
It is well known that plastic materials may be welded to one another by the application of heat. Many prior art devices developed for this purpose are essentially immobile units particularly adapted for mass production requirements in a manufacturing facility.
As suggested above, plastic materials may be welded to one another by application of heat. Numerous devices have been developed for this purpose of which the following descriptions are representative. U.S. Pat. No. 2,529,717 describes an RF energized heat sealer wherein one electrode of a pair of electrodes is removable to accommodate placement of the material to be sealed between the electrodes; a constant RF energy level is applied for a timed duration to effect the seal. U.S. Pat. No. 2,629,809 is directed to a manually operated device for compressing thermoplastic material between an anvil and a hammer whereupon RF energy is applied until the hammer has been raised to a predetermined height. U.S. Pat. No. 2,751,965 illustrates a bag sealer employing a first timing circuit for maintaining compressed the opening of the bag intermediate electrodes and a second timing circuit for applying a fixed level of RF energy. U.S. Pat. No. 3,040,153 illustrates a yarn splicer having a pair of pinchers for compressing yarn ends intermediate fixed position electrodes between which RF energy is transmitted to fuse the yarn ends to one another. U.S. Pat. No. 3,232,810 illustrates the use of a tuned cavity to regulate the transmission of RF energy for sealing polyester materials. U.S. Pat. No. 3,518,396 is directed to a series of resonant circuits which preclude the work piece from altering the heat distribution pattern of a dielectric heating apparatus. U.S. Pat. No. 3,632,943 describes a dielectric heat sealer which incorporates a liquid filled coil as a cooling medium to ensure uniformity of the seals; shield means are also employed to prevent spurious RF leakage. U.S. Pat. No. 3,738,892 illustrates two spaced apart conductive members for inductively heating and welding two adjacent sheets of plastic to one another without an attendant compression of the sheets.
There is a continual existing need for blood donors in order to meet the day to day hospital demands for blood. Consequently, many private organizations, whether or not affiliated with hospitals, have arisen for the sole purpose of collecting blood. In order to obtain sufficient quantities of blood, these organizations must visit locations having a high concentration of blood donors. That is, they must periodically visit schools, office buildings, factories and the like and they must transport all equipment necessary to collect the donated blood.
Normally, the blood is drawn from a donor through flexible tubing extending into a plastic bag. Once the bag is filled to its capacity, the tubing must be sealed to prevent leakage and, more importantly, prevent deterioration of the collected blood. Because of the required mobility and rapid processing of a blood collection unit, any and all equipment required must be specifically designed for compact storage, minimum reliance upon support facilities at the blood collection location, minimum operating and set up times and ease of operability.
Plastic tubing, particularly of the type used in conjunction with the collection of blood, is relatively fragile and is easily burst when heated to a temperature close to its melting point. To effectively and repetitively accurately heat seal or weld such tubing, certain parameters must be observed. The heat applied should be limited to the heat necessary to effect a weld. The locality of the applied heat should be focused upon the actual physical section upon which the weld is to be made to preclude softening of adjacent material as such softening may permit the fluid, under pressure within the tubing, to burst the tubing.
To meet the need for readily and easily sealing blood filled plastic tubing, a hand held operated tubing sealer has been developed and is described in U.S. Pat. No. 4,013,860 entitled “Hand Held Electromechanical Sealer”, assigned to the present assignee and incorporated herein by reference. This sealer is a readily transportable sealer of small size and is hand operated to form heat seals in any plastic tubing placed intermediate its jaws. Thus, it is readily usable to form seals at the donor site prior to withdrawing the needle and maintaining a sterile closed system. Also, a plurality of sealed segregated compartments along a length of tubing filled with blood can be completed, wherein each of the compartments is identified with a common serial number. Thereafter, the compartments may be segregated from one another and various tests may be preformed upon the sample of blood contained in the compartments. This capability is particularly important where testing is necessary and yet maintenance of the seal for the blood within the attendant collection bag is not to be disrupted or broken.
At most blood collection centers, such as those operated by the Red Cross, much of the manual labor is performed as charitable work by older persons. These persons are physically handicapped by the natural processes of aging, by arthritis or by previous injuries. For those persons whose hands are not strong or who suffer pain when they attempt to grip an article with their hands, a hand held sealer is difficult or painful to use. Consequently, the rate of production of seals is essentially slower than optimum. A desk mounted sealer described in U.S. Pat. No. 4,186,292, assigned to the present assignee and incorporated herein by reference, is usable by an operator who is either seated or standing and it provides a direct line of sight for the operator in either position. Thereby, operator fatigue is diminished and accurate positioning of the liquid filled tubing to be automatically sealed is promoted. Through actuation of a tubing position sensing switch or a foot operated switch, a seal will be effected in the tubing placed intermediate a fixed and a movable jaw, thereby allowing the operator to use one or both hands to repetitively place and reposition the tubing intermediate the jaws. The housing for the sealer sealingly encloses the operative elements to preclude seepage of fluid thereinto from a burst liquid filled length of tubing. The shaft supporting the moveable jaw and extending from within the housing is sealed through a wiping seal. The jaws themselves and the attendant structure are developed from large mass heat conducting material to dissipate the heat generated by the jaws and to preclude heat build up for the benefit of both the operator and the integrity of the formed seals.
U.S. Pat. No. 4,390,832, assigned to the present assignee and incorporated herein by reference, describes an RF generating circuit for providing a source of RF energy to seal a length of tubing placed intermediate a pair of jaws. The pair of jaws are electrically connected to the source of RF energy as plates of a variable capacitor in an RF resonant circuit. The flow of RF energy across the pair of jaws, which energy heats the tubing and, in conjunction with mechanical pressure, makes the weld, is a function of timing and of the spacing between the jaws, which spacing affects the degree of resonance of the RF resonant circuit. Simultaneous with the heating of the tubing, the configuration of the pair of jaws compresses the tubing placed therebetween and focuses the RF energy in a narrow swath across the tubing while simultaneously elongating and spreading the tubing at the swath to obtain a leak free weld. The resulting weld is configured to provide for separation of the sealed compartments of the tubing without tearing or rupturing the compartments.
In U.S. Pat. No. 4,529,859, assigned to the present assignee and incorporated herein by reference, a solenoid operated moveable jaw is disclosed which cooperates with a fixed jaw protruding from a blood tubing sealing unit and formed as part of a relatively massive heat sink to effect seals on liquid filled plastic tubing upon transmission of RF energy timed to coincide with a degree of initial mechanical compression of the tubing by the jaws after the movement of the moveable jaw has been triggered by the tubing intercepting and reflecting a beam of light. Dissipation of heat from the exposed parts of the fixed jaw is by convention. Dissipation of heat from the enclosed part of the fixed end moveable jaws and that produced by the circuitry generating the RF energy internal to the sealer unit is effected by channeling the heat by conduction from all internal heat sources to the bottom and rear plates of the unit and dissipating the heat from the bottom and rear plates to the atmosphere by convection.
U.S. Pat. No. 5,750,971, assigned to the present assignee and incorporated herein by reference, discloses the use of RF power for melting, sealing and welding plastic tubing compressed between a pair manually or automatically actuated electrically conducting jaws of a hand held or fixed base tubing sealer. The RF power is regulated by a pulse width modulator controlling the duty cycle of applied constant voltage pulses. A predetermined change of impedance of the tubing during compression and melting is detected to regulate the power applied and to ensure a weld of predetermined physical parameters. On completion of the weld, a first timer is reset and a further weld may be made. In the event of impedance mismatch, a second timer inhibits further application of power and resetting of the first timer. The use of the pulse width modulator enhances conservation of the power and accommodates portability of the tubing sealer through use of rechargeable batteries as the power source.
Each of the tubing sealers described or referenced above, require attendance by an operator during the sealing process. Depending upon the size and material of the tubing to be sealed as well as the rate and level of power applied to effect heating to form the weld, each weld may take tens of seconds or in excess of a minute. At blood collection centers, the use of hand held or desk mounted tubing sealers requires the attendance of an operator for the duration of the seal(s) to be made. For efficiency purposes and to simultaneously harvest as much collected blood as possible from as many donors as possible while engaging as few operators as possible, elimination of operator time to effect a seal(s) is desirable as such an operator can attend to other matters while a seal(s) is being formed.